1. Field of the Invention
The present invention relates generally to the fields of anesthesia and pain management. More specifically, the present invention provides methods for reducing pain by regionally delivering a solution comprising a volatile anesthetic and an extractive solvent to a subject in need of pain reduction or anesthesia.
2. Description of Related Art
Millions of people suffer from pain. The pain may be minor, such as headaches, acute lower back pain, and acute muscle pain, or severe, such as chronic pain. Chronic pain may be associated with cancer treatment, HIV, diabetes, or other conditions. Chronic pain can be difficult to treat, with many chronic pain sufferers noting that their pain is not well controlled with current pain medications or that their medications have significant associated adverse effects (e.g., nausea and vomiting, dependence, tolerance, etc.).
In an attempt to address the problem of chronic pain management, intrathecal infusion pumps and neurostimulators have been developed. Intrathecal infusion pumps are aimed at continuous, or near continuous delivery of liquid anesthetic and/or analgesic agents. Many of these infusion pumps are totally implantable, which helps to reduce the risk of infection when compared to the long-term use of external systems. The infusion pump may also be programmable to allow patients or their clinicians to adjust dosing amounts or daily delivery schedule, helping to meet a patient's changing needs.
Neurostimulators are available in various forms and stimulate nerves to relieve pain. Both intrathecal pumps and neurostimulators have drawbacks, including the onset of tolerance, with the treatments becoming less effective over time. In addition, neither intrathecal infusion pumps nor neurostimulators are suitable for anesthetizing a patient prior to a surgery.
Various approaches for inducing anesthesia or analgesia are known. Systemic delivery of a general anesthetic renders a patient unconscious and unaware of the surgery. In contrast, anesthetics may be applied regionally, for example, to the spine, epidurally, or near a nerve in a nerve block to anesthetize only a portion of the patient's body. For general anesthesia, delivery of a general anesthetic to a patient prior to surgery is typically performed using an initial i.v. injection of an anesthetic followed by intubation and administration of an inhalable anesthetic gas. It is worthwhile to note that the mechanism of action for general anesthesia is still not completely understood.
Considerable negative side effects may result from administration of general anesthesia. A large tube has to be placed into the trachea, which can result in trauma to the upper airway. Many patients report postoperative hoarseness and tenderness of the mouth and throat. In addition, the large amount of gases required to flood the body to reach the targeted organs can have an adverse affect on the non-targeted organs, especially the heart, with an increased risk of cardiopulmonary morbidity during general anesthesia. Especially in the elderly, there is substantial evidence for prolonged cognitive dysfunction following general anesthesia (Moller et al., 1998). Additionally, regional anesthetic techniques appear to lead to less overall morbidity and mortality from cardiopulmonary causes as compared to general anesthesia (Rasmussen et al., 2003; Rogers et al., 2000)
Certain risks are also associated with inhalation administration of a volatile anesthetic, e.g., during general anesthesia. Volatile anesthetic compositions formulated for inhalation generally have relatively low boiling points and high vapor pressures. Volatile anesthetic compositions are often flammable or explosive in both their liquid and vapor states. Further, inhalation of vapors by health care personnel can cause drowsiness, which is not desirable in an operating room environment. Thus, substantial care must be taken to safely handle volatile anesthetics in order to minimize both the risk of inhalation by medical personnel and the risk of fire or explosion, and care must be taken to try to ensure that there is little or no release of the volatile anesthetic into the atmosphere at all stages of handling.
Clearly, there exists a need for improved methods for pain management and regional anesthesia. Further, there exists a need for volatile anesthetic compositions that have reduced risks, as described above, associated with their use. There is also a need for methods for delivering such improved volatile anesthetic compositions, e.g., for treating pain or for use in a surgical procedure.